1. Field of the Invention
An aspect of the present invention relates to a lithium (Li) secondary battery, and more particularly, to a thermally stabilized Li secondary battery in which at least a portion of the inner surface of a secondary battery case includes an ignition inhibitor so as to prevent an internal temperature of the secondary battery from rising to a predetermined temperature or higher.
2. Description of the Related Art
Recently, a large number of compact and light-weighted electric or electronic apparatuses such as cellular phones, notebooks, and camcorders have been actively developed and produced. These portable electric or electronic apparatuses are provided with battery packs, so that they can operate without separate power supplies. A battery pack includes at least one battery to output a predetermined voltage so as to drive the portable electric or electronic apparatuses for a predetermined time.
Recently, the battery pack has employed a rechargeable secondary battery for economic benefit. Examples of the secondary battery include: a nickel cadmium (Ni—Cd) battery; a nickel hydride (Ni-MH) battery; and a Li secondary battery such as a Li polymer battery and a Li-ion battery.
Particularly, the Li secondary battery has an operating voltage of 3.6V which is three times higher than that of the Ni—Cd battery or the Ni-MH battery. In addition, the Li secondary battery has a high energy density per unit weight. Therefore, demand for Li secondary batteries has rapidly increased.
In the Li secondary battery, a Li-based oxide is used as a positive electrode active material, and carbon is used as a negative electrode active material. In general, batteries are classified into a liquid electrolyte battery and a polymer electrolyte battery according to a type of the electrolyte. The Li secondary battery using the liquid electrolyte is called a Li-ion battery, and the Li secondary battery using the polymer electrolyte is called a Li polymer battery. Li secondary batteries are manufactured in various shapes. According to the shapes, the Li secondary batteries are classified into a cylindrical battery, a prismatic battery, and a pouch-type battery.
A Li-ion secondary battery includes: an electrode assembly which is formed by rolling a positive electrode plate coated with a positive electrode active material, a negative electrode plate coated with a negative electrode active material, and a separator interposed between the positive and negative electrode plates to prevent an electrical short between the two electrode plates and allow only Li-ion to pass therethrough; a secondary battery case which accommodates the electrode assembly; and an electrolyte solution which is inserted inside the secondary battery case and allows Li-ion to move.
In the Li-ion secondary battery, a positive electrode plate, on which the positive electrode active material is coated and to which a positive electrode tab is connected, a negative electrode plate, on which the negative electrode active material is coated and to which a negative electrode tab is connected, and a separator, are laminated and rolled so as to obtain an electrode assembly.
The electrode assembly is accommodated in the Li-ion secondary battery case and fastened so as not to be detached. Thereafter, the electrolyte solution is injected into the Li-ion secondary battery case, and, an opening portion of the case is sealed with a cap assembly, thereby constituting the Li-ion secondary battery.
However, heat is generated inside the Li secondary battery at charging/discharging times through an electrochemical reaction. In particular, an internal heating value becomes large when abrupt discharging or over-charging occurs, and thus an internal temperature of the battery rapidly increases. As a result, an internal structure changes, thereby generating an electrical short inside the battery. This causes significant danger such as explosion of the Li secondary battery.